The Campaign object will have a collection of the list(s) associated with the Campaign. The lists are in the the XML node ContactLists. If you're using one of our many open source libraries, it will be returned as an array or container of the List objects so you can pull that from there. If the node is empty, does not exist or the array/collection is empty, the Campaign is currently not associated with any lists. You can see more about this in our documentation found here: http://community.constantcontact.com/t5/Documentation/Campaign-Resource/ba-p/25109
Dave Berard Senior Product Manager, Constant Contact
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